Visa-Free means travellers have not required any visa in order to enter a specific country. All they need is a valid passport to travel.
Visa on Arrival or Border Gate Visa means travellers have required a visa in order to enter a specific country but in this case, they can obtain it upon arrival to the specific country.
Travellers are not required to apply for this visa in advance of their travel. This visa is normally used for short stays within a specific country.